The present invention is related to Japanese patent application No. Hei. 11-366457, filed Dec. 24, 1999; the contents of which are incorporated herein by reference.
The present invention relates to a combustion pressure sensor, and more particularly, to a combustion pressure sensor screwed into a tapped hole formed on an engine.
In JP-A No. H7-139736 a glow plug with a combustion pressure sensor used as a starting auxiliary device for an engine such as a diesel engine or the like is described. A general structural schematic cross sectional view of a conventional glow plug with combustion pressure sensor is shown in FIG. 14A. FIG. 14B shows the outer peripheral shape of the top view of the hexagonal portion 201b of the housing 201 shown in FIG. 14A for comparison with a combustion pressure sensor 30.
A glow plug with combustion pressure sensor J1 is provided with a plug body (unique to the glow plug) 200 that holds a heater 206 (heated when a current is supplied in the housing 201) a combustion pressure sensor (pressure sensor) 30 fixed to the plug body 200 for detecting a combustion pressure in an engine based on combustion pressure force exerted on the plug body 200, and a lead wire 500 outputting a signal from the combustion pressure sensor 30.
One end of the plug body 200 is inserted into a tapped hole 1b formed on an engine head 1 of a diesel engine. The plug body 200 is screw-fixed to the engine head 1. For the screw fixing, a fixing screw 201a formed on the outer peripheral surface of the housing 201 of the plug body 200 is screwed by turning the plug body 200 round the axis by means of the hexagonal portion 201b formed on the other end of the housing 201.
The spark plug function of the glow plug J1 will be described herein under. A voltage is applied to a middle shaft 204 from a power source though a connecting bar 2, and earthed to the engine head 1 through a heater coil 203, a sheathed tube 202, and the housing 201. Thereby, the heater 206 comprising the heater coil 203 and sheathed tube 202 is heated for auxiliary ignition starting of the diesel engine.
The combustion pressure sensor 30 is a ring-shaped component having a through hole 30a and an inside screw portion 311. The plug body 200 is inserted into the through hole 30a, and the combustion sensor 30 is fixed to the fixing screw 201a of the plug body 200 by means of screw fixing. Furthermore, the one end of the lead wire 500 is connected electrically to the top end surface of the combustion pressure sensor 30 with interposition of a fixing metal member 333. The other end of the lead wire 500 is provided with a connector 400 for connecting to an external terminal for leading out the sensor signal to the external (ECU or the like of a vehicle).
The combustion pressure is detected as described herein. A combustion pressure generated in a combustion chamber 1a is transmitted to the fixing screw 201a through the heater 206 and the housing 201. Because the housing 201 is pushed up in the axial direction of the screw hole 1b and concomitantly deformed slightly, the load of the combustion pressure sensor 30 is relaxed. The sensor 30 converts the load change to an electrical signal and thus the combustion pressure is thereby detected.
A sequential work for attaching the glow plug with combustion pressure sensor J1 will be described with reference to FIG. 15 and FIG. 16. The combustion pressure sensor 30 is inserted previously along the fixing screw 201a of the housing 201 of the plug body 200 to attach the combustion pressure sensor 30 temporarily. At that time, because the outside diameter of the hexagonal portion 201b of the plug body 200 is larger than the inside diameter of the through hole 30a of the combustion pressure sensor 30 as shown in FIG. 14B, the plug body 200 is inserted into the through hole 30a of the combustion pressure sensor 30 from the heater 206 side (the insertion side to the screw hole 1b).
The plug body 200 is inserted into the screw hole 1b of the engine head 1 in this state, the hexagonal portion 201b is turned round the axis by use of a plug wrench 900 (refer to FIG. 15), only the plug body 200 is fastened to the screw hole 1b for holding and fixing. Then, the hexagonal portion 312 of a nut of the combustion pressure sensor 30 is turned round the axis along the fixing screw 201a of the housing 201 for fastening to hold and fix the bottom surface of the combustion pressure sensor 30 against the pedestal surface (surface) 1e of the engine head 1.
However, as the result of examination of the sequential attachment of the conventional glow plug J1 conducted by the inventors of the present invention, the problem described herein under was found. The hexagonal portion (nut portion) 201b of the plug body 200 into which a plug wrench 900 is inserted is located as close as possible to the lead wire 500 and the fixing metal member 333 of the combustion pressure sensor 30.
The reason why these components are located so close as described hereinabove is that addition of the vibration noise (for example, the frequency is 5 kHz or lower) generated from the plug body 200 itself to the combustion pressure detected by means of the combustion pressure sensor 30 is reduced more as the top end surface of the hexagonal portion 201b of the plug body 200 is located closer to the top end surface of the hexagonal portion 312 of the combustion pressure sensor 30. Specifically, as the length of the portion not held and fixed by means of other member and opened out of the plug body 200 is shorter. The close location is the important factor for securing the performance.
Therefore, in fastening the plug body 200, when a plug wrench 900 is fit on the hexagonal portion 201b as shown in FIG. 15, the end of the plug wrench 900 can touch the lead wire 500 and break the lead wire 500 due to bending or nicking or deformation or breaking of the fixing metal member 333.
Careful and cautious work is required to avoid interference between the plug wrench 900 and the lead wire 500 of the combustion pressure sensor 30 and entanglement between the lead wire 500 and the connector 400 and the portion around the engine.
As described hereinabove, when the glow plug J1 has a conventional combustion pressure sensor, there are workability and working efficiency problems due to the lead wire 500 connected to the combustion pressure sensor 30. Such problems are common not only for the glow plug with combustion pressure sensor but also for a structure that is screw-fixed to a screw hole formed on an engine by turning the one end of the structure that has been inserted into the screw hole round the axis and a combustion pressure sensor provided with a combustion pressure sensor attached to the structure (simply referred to as combustion pressure sensor hereinafter).
It is therefore an object of the present invention to improve the workability in forming a combustion pressure sensor without adverse effects on a lead wire connected to a combustion pressure sensor.
To accomplish these and other objects, the invention described in a first aspect provides a combustion pressure sensor characterized in that the outer diameter of the end including the nut portion of the structure inserted into the screw hole is smaller than the inside diameter of the through hole of the combustion pressure sensor. Therefore, the structure can be inserted into the through hole of the combustion pressure sensor from the other end of the structure.
In the present invention, because the structure can be inserted from the nut portion side end (the other end), the sensor can be attached to the structure after the structure has been screw-connected to the screw hole of the engine. Therefore, the adverse effect of the lead wire connected to the combustion pressure sensor is eliminated. Therefore the workability is improved when the combustion pressure sensor is formed.
In another aspect, the lead wire for outputting the signal of the combustion pressure sensor to the external (ECU or the like) is detachable from the combustion pressure sensor. Thereby, the lead wire is detachable from the combustion pressure sensor. Because the lead wire is attached to the combustion pressure sensor after the structure has been screw-connected to the screw hole of the engine, workability is improved without adverse effect of the lead wire connected to the combustion pressure sensor when the combustion pressure sensor is formed. In another aspect, the lead wire is detachable from the combustion pressure sensor by means of the screw connection.
In another aspect, the combustion pressure sensor has a cutout portion formed by cutting from the outer periphery to the inside on the combustion pressure sensor. The combustion pressure sensor is disposed so that the cutout portion is fitted to the structure. Thereby, because the combustion pressure sensor can be attached after the structure has been screw-connected to the engine, the workability is improved without any adverse effect of the lead wire connected to the combustion pressure sensor when the combustion pressure sensor is formed.
In another aspect, the screw portion is formed on the inside surface of the through hole of the combustion pressure sensor into which the structure is inserted, and the screw portion of the structure is screw-connected to the screw portion of the though hole to thereby fix the combustion pressure sensor to the structure (the inventions described in the second aspect and a fifth aspect).
In another aspect, the combustion pressure sensor can be fixed to the structure by the axial force of the separate nut, which is a separate member from the combustion pressure sensor, that is screw-connected to the screw portion of the structure. In this case, it is not necessary to form the screw portion on the combustion pressure sensor.
In another aspect, the lead wire is connected to the combustion pressure sensor to be drawn out from the direction different from the action direction of the axial force of the separate nut. Thereby, the interference between the separate nut and the lead wire is prevented efficiently.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In the drawings: